Service Level Agreements and Vendor Management

During the post-bubble crash, many organizations started using vendor management programs as a cost control measure. This worked great for managing costs where the unit of measure is well defined, or there is an iron-clad service level agreement. However, the jury is very much out on whether vendor management is the right way to manage relationships with consultants, since it is unlikely that a procurement officer working in the vendor management office understands the nuanced difference between various consultants, especially where a pre-existing relationship exists between the buyer and the consultant.

What is your experience? Has vendor management added long term value to the consulting relationships you have?